Machine and method for etching curved plates

ABSTRACT

A PROCESS AND APPARATUS FOR POWDERLESS ETCHING BY PADDLE MEANS OF CURVED PRINTING PLATES WHICH INCLUDES AN ADDITIONAL ARRAY OF SPRAY NOZZLES AT EACH SIDE OF THE PLATE HOLDER.

M. H. FISHABER ET AL 3,573,119

March so, 1971 MACHINE AND METHOD FOR ETCHING CURVED PLATES Filed March 5, 1969 5 Sheets-Sheet z INVENTORS. Marl/fr? H His/20b er" JOHA N NE 5 filafrnbqck HTTOANEY March 30, 1971 F|$HABER ET AL 3,573,119

MACHINE AND METHOD FOR ETCHING CURVED PLATES Filed March 5, 1969 5 Sheets-Sheet 5 I lN'yENToRs. Marv/n 6. F/shaber JOHA N NES E Lain 2190c M 2 Mia IQTTOIQNEY March 30, 1971 HSHABER ETAL 3,573,11

MACHINE AND METHOI D FOR ETCHING CURVED PLATES Filed March 5, 1969 5 Sheets-Sheet 4 INVENTORS. Marv/0h. Fl'shaber' Jfll/A IVA/ES E mlmo c/ HTTORNEY MACHINE AND METHOD FOR ETCHING CURVED PLATES Filed March 3, 1969 L A W E B A H B F H M 5 Sheets-Sheet 5 3 m6 T 0 0 .5 W. H m M L/Of/A/VNES F. La/i'nbock ATTORNEY United States Patent 3,573,119 MACHINE AND METHOD FOR ETCHING CURVED PLATES Marvin H. Fishaber, Saginaw, Mich, and Johannes F. Laimbock, Rotterdam, Netherlands, assignors to The Dow Chemical Company, Midland, Mich.

Filed Mar. 3, 1969, Ser. No. 807,165 (Filed under Rule 47(a) and 35 U.S.C. 116) Int. Cl. B41n 3/02; C23f 1/02 US. Cl. 156-14 12 Claims ABSTRACT OF THE DISCLOSURE A process and apparatus for powderless etching by paddle means of curved printing plates which includes an additional array of spray nozzles at each side of the plate holder.

BACKGROUND OF THE INVENTION 1) Field of the invention (2) Description of the prior art According to prior methods of powderless etching curved plates, successive increments of etching composition have been brought to the curved plate in various ways. Some have attempted to employ solely dipping paddles. Others have employed solely sprays from spray nozzles.

In general, the prior art methods and apparatus, employing solely paddles or solely spray nozzles, suffer from the inability to provide the appropriate depth of etch while obtaining shoulders of uniform angular inclination, the shoulder portions extending circumferentially of the curved plate being formed at a wider angle and being thus broader or more elongated than the shoulder portions extending longitudinally of the curved plate. This unevenness of shoulder can result in undercutting of the longitudinal shoulder portions while at the same time the circumferential shoulder portions are excessively broad so as to cause smudgy printing of the image.

Apparatus that provides for directing arrays of small streams of etching composition to rotating paddles that in turn flip the composition as a spray or splash to the curved plate, is more fully described in the co-pending application of Clayton W. Hoornstra, Ser. No. 640,562, filed May 23, 1967.

(3) Definitions Shoulder angle, as used herein, refers to the angle the shoulder or sidewall of the relief image makes with a line normal to the metal plate in general and extending through the edge of the relief image.

Counter-rotating, dipping, outwardly and upwardly discharging, paddles, as used herein, refers to a pair of spaced-apart counter rotating, dipping, vaned paddles having horizontal and substantially parallel axes of rotation and means to rotate the paddles in such a manner that the vanes of each paddle, while making the closest approach to the other paddle, are moving downwardly. Such paddles are to be distinguished from counter rotating paddles with means for rotating the paddles so that the vanes at closest approach are moving upwardly whereby the pair is centrally upwardly discharging of splashed liquid.

For the purposes of the following description and the appended claims, reference to an array of spray nozzles at one side of a curved plate and holder being substantially mutually opposed to an array of spray nozzles on the opposite side means that the nozzles in the first array are pointed in a first direction toward a line parallel to the axis of rotation of the plate holder which first direction has a component toward a first end of the plate holder, while the nozzles in the opposite array are pointed in a second direction toward a similar line, which second direction has a component toward the second end of the plate holder. In the specific case where all nozzles are pointed at an agle of degrees to a line parallel to the axis of rotation of the plate holder and also comply with the foregoing description, nozzles on opposite sides are clearly mutually opposed along parallel lines.

OBJECTS OF THE INVENTION An important object of the invention is to provide improved apparatus for powderless etching of curved metal plates by means of which curved plates can be etched so as to form shoulders of substantially uniform angle or inclination all about each relief image.

Another object of the invention is to provide apparatus for powderless etching of curved metal plates whereby plates etched in the apparatus exhibit (l) shoulders of substantially uniform angles and (2) open areas that are substantially free from pimpling.

Yet a further object of the invention is to provide an improved method of powderless etching of a curved plate whereby etched images are obtained having shoulders of substantially uniform angles all around each image and narrow enough to avoid smudging during printing.

SUMMARY OF THE INVENTION The stated objects of the invention are met by a specific combination of parts which together provide an improvement in apparatus for powderless etching and also by a specific mode of bringing increments of etching composition to a curved plate to be etched. The improvement lies (within an etching machine for powderless etching of curved plates, the machine comprising a substantially enclosed housing having disposed therein a rotatable holder for a curved plate to be etched, a sump for a powderless etching composition, means for directing increments of the etching composition against a. curved plate held by the said rotatable holder, and associated with the enclosed housing, means for stirring or agitating the etching composition, means for cooling the etching composition, with or without means for controlling the depth of the etching composition in the sump utilizing a. second vessel or reservoir, and means for rotating the plate holder) in improved means for directing successive increments of the etching composition against a curved plate held by the said rotatable holder which comprises:

(1) At least one pair of counter-rotating, dipping, outwardly and upwardly discharging, paddles mounted below the plate holder and adapted to dip into etching composition in the sump and to throw such successive increments of etching composition against at least the lower portion of each laterally exposed side of a curved plate held on the plate holder,

(2) At least one substantially linear array of spray nozzles mounted at each side of the plate holder above the axis of rotation thereof, each array being substantially parallel to the axis of rotation of the plate holder, substantially each of the nozzles being mounted to emit spray with the center of the spray pattern directed at a preselected angle in the range of about 10 degrees above horizontal to 40 degrees below horizontal, and at an included angle of from about 15 to 60 degrees with respect to a line parallel to the axis of rotation of the plate holder, nozzles on opposite sides of the plate holder being substantially mutually opposed, and

(3) Means for supplying etching composition to the nozzles, such means including a pump, supply piping means to and from the pump, and manifold means for each array, each such manifold means being connected to the supply piping means which is fed by the pump.

The improvement in the method of powderless etching lies in simultaneously bringing successive increments of etching composition directly from an underlying sump to the curved plate, while it is rotating, while also directing successive increments of etching composition at the laterally exposed sides of the curved plate in linear arrays of spray patterns at the angles and in the specific manner described herein which avoids gross variation of shoulder angles in each direction around each relief image.

The orifices of spray nozzles on opposite sides, respectively, of the curved plate are substantially mutually opposed, except that opposing sprays are preferably staggered alternately as to spacing along the manifolds. Within each linear array, the spray nozzles are aimed in substantially parallel directions.

In one of the specific embodiments of the invention an additional array of spray nozzles is provided directly underneath the curved plate and between the dipping paddles, and a baffle at each side of the spray pattern is preferably employed to minimize interference therewith by splash from the clipping paddles.

In another specific embodiment a dual array of nozzles is provided at each side, as well as underneath, the curved plate and array is emitted substantially continuously from each dual array, but mutually exclusively, in each case, from first one array and then the other of each pair, in a cyclical, alternating manner.

The nozzles employed may be designed to throw most any pattern, round, square, rectangular or elliptical, preferably of uniform density throughout the pattern. Nozzle spacing is appropriate to provide at least some overlap of round or square patterns. In the case of rectangular or elliptical patterns, it is preferred that the long dimension, or major axis, of substantially each of the patterns is tilted to an angle of from about to 85 degrees from the horizontal direction, the long dimensions or major axes of the patterns in each array, respectively, being substan tially parallel.

DETAILED DESCRIPTION OF THE DRAWINGS The apparatus of the invention will be more clearly understood with reference to the drawings in which like reference numerals refer to like parts and in which:

FIG. 1 is a side view mostly broken away and in section showing an embodiment of the apparatus of the invention;

FIG. .2 is a view in section, taken along line 2-2 of FIG. 1, showing the profile of the enclosed housing and the relative disposition of the plate holder, the spray nozzles and the dipping paddles in the embodiment of FIG. 1;

FIG. 3 is a schematic, fragmentary plan view of the nozzle arrays of the apparatus of FIG. 1 showing the individual nozzles disposed at the lateral sides of a curved plate to be etched;

FIG. 4 is a schematic, fragmentary side view of a curved plate to be etched showing typical tilted elliptical spray patterns on the surface of the curved plate;

FIG. 5 is a view in transverse section of a portion of a manifold at one side of the curved plate showing a single spray nozzle in full and the divergence transverse to the minor axis of an elliptical spray pattern emitting therefrom;

FIG. 6 is a fragmentary view in plan of the same portion of a manifold having a single nozzle thereon as in FIG. 5 and showing the divergence transverse to the major axis of an elliptical spray pattern emitting therefrom;

FIG. 7 is a view in section similar to that of FIG. 2 showing the apparatus of another embodiment of the invention in which a single array of spray nozzles is employed beneath the curved plate, in addition to the arrays at the side;

FIG. 8 is a view in section similar to that of FIG. 2 showing still another embodiment of the apparatus of the present invention in which a dual array of nozzles is used at each side and beneath the curved plate; and

FIG. 9 is a fragmentary view in plan taken along line 99 of FIG. 8 showing a portion of one of the dual arrays of nozzles of FIG. 8 and illustrating a suitable arrangement of manifolds and alternately directed nozzles.

Referring more particularly to FIGS. 1 and 2, the present apparatus for the powderless etching of curved plates is seen to consist of an enclosed housing indicated generally by the numeral 10, a sink indicated generally by the numeral 11 for descumming, rinsing and draining a curved metal plate 12 held by a plate holder 13, a sump 14 in housing 10 for etching composition 15, a reservoir 16 for receiving overflow of composition 15,

" and fluid conveying means 17 for returning etching composition from reservoir 16 to sump '14.

The enclosed housing 10 is provided with end walls 18 and 19, side walls 20 and 21, a roof or cover 22 having a hinged lid 23 therein and a bottom wall 24.

The lower portions of the end walls 18, 19 and the side walls 20, 21 and the bottom wall 24 of the enclosed housing '10 together form the sump 14 that holds powderless etching composition 15.

In end 'wall '18 of the enclosed housing 10 there is provided an opening (not shown) for admitting and removing the plate holder 13. The opening is closed by any suitable means such as a vertical sliding door 25 that slides between vertical guides or flanges 26 at either lateral edge of the said opening.

The plate holder may be of any suitable construction for supporting a curved plate and rotating it horizontally on its axis of curvature While it is being etched, such a curved plate generally having the form of a partial or complete, longitudinally slit, cylindrical shell. The plate holder may be a mandrel with several axially spaced radially extending groups of spokes or arms to the ends of which the curved plate is attached. Sometimes three or more longitudinal members or interconnecting bars are mounted on such spokes and the curved plate is clamped to such longitudinal members or bars. A convenient assembly here illustrated employs a highly perforated and slotted cylindrical shell, almost a screen, of pro-selected diameter for the size of curved plate contemplated, held about a mandrel by radially extending arms of adjustable radius. The arms may be adjusted to hold a cylindrical shell of a discrete diameter within a reasonable range of useful diameter sizes. The perforations allow etching composition to drain through freely where the shell is not covered by the curved plate and the slots permit ready adjustment of mounting clamps to accommodate different sizes of curved plate.

Referring more particularly to FIG. 2, the plate holder 13 is seen to consist of a cylindrical shell 27 supported concentrically about an axial shaft 28 by radial arms 29 of adjustable length, the axial shaft 28 being journalled at each end in a bearing block or body 30 mounted on the upright end 31 of an inverted T-shaped support member 32. Each T-shaped support member 32 is provided with rollers 33, at the ends 34 of the T-shaped portion, which run on a track 35, generally formed from angle shaped structural members, positioned to guide the plate holder into and out of the enclosed housing 10.

Such tracks are substantially coextensive with the sink 11 and the interior of the enclosed housing 10, being interrupted sufiiciently for operation of the vertical sliding door 25. The tracks have been omitted from FIG. 1 in order to simplify illustration of the invention.

Driving means for the plate holder are provided in the form of a reversible drive electric motor 36 that is mounted outside the enclosed housing 10 on side wall 19 with the shaft thereof coupled to an axial shaft engaging coupler unit 37 that extends through said side wall and is journalled therein. Coupling means 38 on the end of the coupler unit 37 inside the housing, such as a pair of cylindrical sockets or depressions formed in the end face, are adapted to receive and engage the end structure 39, such as a pair of cylindrical prongs, f the axial shaft 28 of the plate holder 13 and to cause rotation of the mandrel when the drive motor 36 is energized.

An opening 40 in the lower part of end wall 19 of the enclosed housing provides for overflow of etching composition from the sump '14 to the associated reservoir 16. The level of etching composition 15 in the sump 14 is regulated by an adjustable weir 41 that is raised or lowered by mannually rotating the externally threaded shaft 42 using the externally accessible handwheel 43.

In the sump '14 are provided mixing means 44, refrigeration coils 45 connected to a refrigeration system (not shown), means 46 for draining the sump, and supply piping means 47 for conveying etching composition from the fluid conveying means 17 to the headers or manifolds 48 holding the spray nozzles 49. Generally heating means is also provided within the sump, especially if the machine is not in an environment that is likely always to be at a temperature of about C. or higher.

Ordinarily, and very desirably, the level of etching composition 15 is the sump 14 is carefully controlled by means of the adjustable weir 41 to regulate the amount of splash from the dipping paddles. The weir may be adjusted to a higher or lower level by turning the handwheel 43 that is mounted on the shaft 42. The shaft 42 threadably engages brackets 50 which hold the weir 41. The weir 41 is best adjusted so that the paddles dip into the etching composition from about 0.25 to 0.75 inch at each revolution.

Etching composition 15 flowing out of the sump 14 over the weir 41 is, during start up of operations, drawn into an inlet 51 in the bottom of reservoir 16 by the action of pump 52 (shown schematically) whence the composition is pumped through a line 53 into the sump 14 to the line 44 which is perforated with numerous holes through the wall thereof and issuance of composition therefrom under pressure causes substantial turbulence and mixing of the composition so as to disperse the water and waterimmiscible phases of the etching composition 15. Generally, it is suitable to employ pipes with perforations about 3 to 4 millimeters in diameter and to supply etching composition at 2 to 3 pounds per square inch gauge. It is to be understood that the number of perforated pipes and refrigeration coils is normally several times greater than here illustrated, the number having been reduced to simplify illustration of the inventive aspects of the present apparatus.

Etching operations may be conducted in the present apparatus without a reservoir and an adjustable weir but is simply less convenient since it is generally necessary to make additions to the etching composition, from time to time, such as nitric acid, solvent or bath extender. In making such additions, care must be taken to avoid changing the depth of the composition in the sump to the extent that the character of splash patterns is materially changed. On the other hand, sufl'lcient depth must be maintained to get adequate splash from the paddles to throw a substantial amount of composition on the plate to be etched.

The use of a reservoir and an adjustable weir is taught and claimed in copending application, Ser. No. 683,409, filed Nov. 15, 1967.

During etching operations after the etching composition is well mixed, the plate holder 13, with a curved plate 12 to be etched mounted thereon, is advanced on its track into the enclosed housing 10 until coupler engaging end structure 39 on the forward end of axial shaft 28 engage coupling means 38 connected with the reversible drive electric drive motor 36 and that motor is started up.

Etching composition is then projected toward the curved metal plate in several ways in a special manner and substantially continuously until etching of the plate is completed.

The etching composition during etching is, in part, splashed up to the plate 12 on plate holder 13 by dipping paddles 54 that are rotated by electric motor drive means 55 and a belt drive 56. Etching composition is also essentially brought to the curved plate 112 to be etched by etching composition pumped from reservoir 16 by pumping means 57. Such etching composition is conveyed through supply piping means 47 to dual manifolds 48 in the enclosed housing 10 as more particularly illustrted in FIG. 2. The piping means 47 divides within the sump 14 to provide etching composition to each manifold 48. Etching composition brought to the manifolds 48 is discharged through nozzles 49 towards the plate 12 to be etched, drains therefrom into the sump 14 and overflows past weir 41 to the reservoir 16. Mixing of the etching composition by pumping some of it through the perforated pipe 44 normally is continued throughout etching operations.

The etching composition 15, may be an aqueous nitric acid composition containing a suitable filming agent and a water immiscible organic liquid, for example, the etching composition described in US. Pat. 3,152,083 or any other liquid composition suitable for powderless etching a curved metal plate having a photoresist thereon. Such compositions must be appropriately stirred or otherwise actively agitated, as by pumping through perforated pipes in order to disperse the water-immiscible portion. The temperature is best regulated as by heating or cooling, as necessary, in order to bring the temperature to and maintain it, at about 68 to 72 F. After commencing rotation of the curved plate and plate holder, generally at a low rate such as 20 to 60 revolutions per minute, preferably with periodic reversal of direction of rotation, e.g. every 0.1 to 2 minutes, rotation of the clipping paddles 54 is commenced, generally at a speed in the range of 300 to 800 revolutions per minute, and pumping of the etching composition to the manifolds and nozzles is carried out.

As an essential aspect of the invention the nozzles are positioned in a critical manner and the sprays emitting therefrom are directed in a critical manner in Order to avoid the radially variegated or unsymmetrical pattern of shoulder elongation that has troubled users of prior apparatus, while avoiding roughness or pimpling of open areas in the finished etched product. As seen in FIG. 2, the array of nozzles 49 is disposed at either side of the curved plate 12 at a level above the axis of curvature thereof, and more generally adjacent the upper edge of the curved plate as it is disposed horizontally. The nozzles direct spray about a line from each nozzle to the plate, which line may be in a range of from about 10 degrees above horizontal to about 40 degrees below horizontal but more preferably is about horizontal to 30 degrees below the horizontal direction. An angle of about 21 degrees is most preferred where no sprays are employed beneath the plate, i.e., between the dipping paddles.

Referring more particlularly to the schematic drawing in FIG. 3, it will be understood that in the horizontal plane, the nozzles direct spray at the curved plate at an included angle of from about 15 to 60 degrees with respect to a line parallel to the axis of rotation of the plate holder. More preferably the included angle is about 25 to 50 degrees. An angle of about 45 degrees is practical and appears optimum, considering such factors as space requirements as well as performance.

The individual nozzles are each provided with a preselected type nozzle of an appropriate design or shape to throw a desired kind of spray pattern. Such patterns, e.g., may be square or rectangular or they may be elliptical like the patterns shown in FIG. 4. Ideally, the spray coverage is uniform in density throughout the plate area receiving spray. As a practical matter, the ideal is approached, but not reached, because most commercially available nozzles do not throw a pattern with a completely uniform density. It has been found best to have the spray patterns substantially meet with preferably a rather slight overlap. Wherein nozzles throwing elliptical patterns are used, such patterns having a major and a minor axis, it has been found advantageous to mount the nozzles so that the major axis of each elliptical pattern is inclined away from the vertical towards the horizontal as illustrated in FIG. 4. The angle of inclination with the horizontal should be in the range of about to 85 degrees and is more preferably about 25 to 65 degrees. The most preferred angle of inclination is about 45 degrees. Within each array, the major axes are inclined substantially parallel.

In using nozzles which emit an elliptical or other elongated pattern such as an elongated rectangle, the angle of divergence of the spray transverse to the major axis, e.g., the angle illustrated in FIG. 6, may be in the range of about 5 to 90 degrees and more preferably is about 30 degrees. The angle of divergence of the spray transverse to the minor axis, i.e., along the major axis as illustrated in FIG. 5 may be in the range of about to 150 degrees, and more preferably is about 90 degrees.

Referring again to the schematic representation in FIG. 3, the nozzles in respective arrays on opposite sides of the curved plate are substantially mutually opposed, i.e., the nozzles in one array are rotated partially towards one end of the curved plate, while the nozzles in the other array are rotated partially towards the opposite end of the curved plate. As a consequence of such disposition of the nozzles, the sprays therefrom tend to move etching composition, clinging to the curved plate, towards opposite ends of the plate. Generally it is also preferred to reverse the direction of rotation of the plate holder about every 6 to 60 seconds, more preferably about every 12 to 24 seconds.

In another embodiment of the apparatus of the invention as illustrated in FIG. 7, an additional array 58 of spray nozzles is disposed horizontally between the counter rotating, dipping paddles 54 and below the curved plate 12. Preferably the tracks 59 for the rollers 60 of the plate holder frame 61 are positioned above, closely adjacent, and inwardly from the paddle, in each case, to serve as baflles to minimize or prevent the splash of the paddles from interfering with the action of the sprays emanating from the array of nozzles 58. If the tracks are not so positioned, then baffles per so, must be positioned adjacent the paddles to prevent interference with spray action from the nozzles 58.

In yet another embodiment of the invention, as illustrated in FIG. 8, a dual array 62, 63 of spray nozzles on duel manifolds 64, 65 supplied by duplicate supply lines 66, 67 leading from a three-way pulsed valve 68 are provided below the plate holder 13 as well as at either side thereof. The side nozzles 62, 63 are installed in such a manner that about half 62 are supplied by one manifold 64 and generally face one end of the curved plate, and the remaining half 63 are supplied by the other manifold 65 and face, generally, the other end of the curved plate, e.g., in the manner illustrated in the fragmentary plan view of FIG. 9.

Any sturdy, controllable three-way valve will do such as the three-way solenoid valve of stainless steel construction supplied by Automatic Switch Company of Florham Park, N.J., Catalogue No. 27 and described in their bulletin No. 8320.

By means of such solenoid valve control, spraying from respective manifolds in each pair of manifolds is alternated in a mutually exclusive, cyclical manner as to each manifold in a given array, while maintaining a substantially continuous emission of spray from each dual array,

overall, during etching. Directional spray cycles may be varied in duration in the range of about 10 seconds to 2 minutes but more preferably are in the range of about 15 to 45 seconds per complete cycle. The use of dual arrays of nozzles with cyclic alternating directional spraying is preferred as giving rise to the most uniform shoulder angles believed obtainable with an etching machine having a plate holder with a fixed axis of rotation. Uniformity here refers to uniformity in each radial direction out from each relief image.

In the embodiments illustrated in FIGS. 7 and 8, it is preferred to use nozzles, in the array or arrays below the curved plate, that throw substantially square patterns, though the remaining nozzles may throw the same, or eliptical, or elongated rectangular, patterns. The side nozzles are preferably positioned to project sprays along a line from each nozzle to the plate which line makes an angle with the horizontal of from about 10 degrees above the horizontal direction to about degrees below horizontal, but most preferably at about the horizontal direction.

Since it is essential that no part of the curved plate to be etched is no more than momentarily away from the zones of spray impingement, the elevation, angle and spacing of the side nozzles from the plate holder are carefully selected to provide substantially continuous spray coverage across the top of the curved plate. If the time gap is too large wherein a given surface area is not being impinged by etching composition, the residual etching composition on that area forms an adherent film over the exposed metal and selective etching substantially stops.

We claim:

1. In a method of etching a curved metal plate in an etching machine in which successive increments of etching composition are projected against said curved plate while said curved plate is rotated about its horizontally disposed axis of curvature with periodic reversal of direction of rotation, the improvement which comprises:

simultaneously projecting successive increments toward the lateral sides and the underneath side of the curved plate;

the increments projected against the lateral sides being essentially in the form of a fine spray projected from above the axis of curvature of the curved plate at an angle in the vertical palne of from about 10 degrees above horizontal to about degrees below horizontal, and in the horizontal plane at an angle of from about 15 to 60 degrees to a line parallel with said axis of curvature;

the projection of successive increments of etching composition against the underneath side of the curved plate from therebelow being along substantially vertical lines as well as along a first and second set of lines extending at an angle of about degrees with respect to a line parallel to the axis of curvature, said first set of lines being substantially normal to the second set of lines and increments being projected along each line in an alternating, repeating and mu tually exclusive manner;

the projection of successive increments toward the lateral sides being carried out by first projecting successive increments as a fine spray from each lateral side of the curved plate in a first set of substantially mutually opposed directions, each direction having a component toward an end of the curved plate, then projecting successive increments as a fine spray from each lateral side in a second set of substantially opposed directions, each direction having a component toward an end of the curved plate, for a given lateral side the components of the first and second sets being towards opposite ends, respectively, of the curved plate, and said projecting in each set of directions being repeated alternately, successively and mutual y exclusively,

the projecting of successive increments toward the curved plate from each of (1) each lateral side, (2) vertically from underneath and (3) at an angle from underneath, being overall substantially continuous.

2. The method as in claim 1 in which the successive increments from each lateral side are projected at an angle in the vertical plane of about horizontal to about 25 degrees below horizontal, and in the horizontal plane at an angle of about 25 to 50 degrees with respect to a line parallel to the axis of curvature.

3. The method as in claim 1 in which the increments from each lateral side are projected only in the first set of directions and only vertically from below the curved plate.

4. In an etching machine for the powderless etching of a curved metal plate in which there is provided: a rotatable plate holder on which the curved plate is mounted substantially horizontally within an enclosed housing above an underlying sump for aqueous powderless etching composition; means for stirring and for controlling the temperature of the powderless etching composition; and means for bringing successive increments of powderless etching composition from the sump to the curved palte; improved means for bringing said successive increments to the curved plate which comprises:

a pair of spaced-apart, counter-rotating,

paddles; at least one substantially linear array of spray nozzles mounted on and communicating with a manifold at each lateral side of the curved plate, the nozzles being aimed at the curved plate in a specific manner;

and liquid conveying means for returning powderless etching composition from the sump to a pump and supply piping means for supplying powderless etching composition from the pump to the manifolds;

said dipping paddles being outwardly and upwardly discharging, extending substantially parallel to the curved plate and substantially symmetrically spaced therefrom, and dipping at least slightly into the powderless etching composition;

said specific manner of aiming the nozzles at the curved plate being characterized in that the nozzles have orifices opening towards the curved plate above the level of the axis of rotation of the curved plate, the nozzles being further directed (1) toward the curved plate (a) at an angle in the vertical plane of from about degrees above the horizontal direction to about 40 degrees below horizontal and (b) at an included angle, in the horizontal plane, of about to 60 degrees with respect to a line parallel to the axis of rotation of the curved plate; (2) so that the spray patterns formed on the curved plate by each array, respectively, are substantially contiguous; and (3) so that the nozzles in a given array at one side of the curved plate are substantially mutually opposed in direction to the direction of an array on the other side of the curved plate.

5. The improvement in an etching machine as in claim 4 in which the nozzles are directed at an angle in the vertical plane in the range of horizontal to about 30 degrees below horizontal and at an included angle, in the horizontal plane, of about 25 to 50 degrees.

6. The improvement in an etching machine as in claim 4 in which the nozzles are shaped to emit elongated spray patterns each having a major axis, and the major axes in each array, respectively, being substantially dipping 10 parallel and inclined from about 5 to degrees from the horizontal direction.

7. The improvement in an etching machine as in claim 6 in which (a) the nozzles are directed (1) along the vertical plane at an angle of about 22 degrees below the horizontal direction and (2) along the horizontal plane at an included angle of about 45 degrees with respect to a line parallel to the axis of rotation of the curved plate, and (b) the elongated spray patterns are inclined at an angle of about 45 degrees from horizontal.

8. The improvement in an etching machine of claim 4 equipped with a communicating reservoir into which at least part of the etching composition in the sump flows by gravity, an adjustable weir being interposed between the sump and the reservoir thereby maintaining the depth of etching composition in the sump at a predetermined level, and etching composition is pumped from the reservoir to the manifolds.

9. The improvement in an etching machine as in claim 4 in which there is also provided at least one array of spray nozzles mounted underneath the plate holder above the etching composition in the sump and between a spaced-apart, dipping paddles, the spray nozzles are directed upwardly toward the plate holder at an angle of about 45 degrees with respect to a line parallel to the axis of rotation of the plate holder, and the nozzles are each mounted on and in communication with a manifold that communicates with said supply piping means.

10. The improvement in an etching machine as in claim 9 in which each at least one array of nozzles is a dual array at either side as well as underneath the plate holder, each array having .a manifold therefor, and the pump and liquid conveying means for supplying powderless etching composition to the manifolds being controlled by valving and valve control means to supply etching composition first to one array of each dual array constituting one set, and then to the other array of each dual array constituting a second set, each array in a given set being supplied simultaneously, the two sets being supplied alternately, cyclically and mutually exclusively, each array in a dual array being disposed to project spray in a direction having a component towards an end of the plate holder and the other array being disposed to project spray in a direction having a component towards the opposite end of the plate holder, and the arrays at either side of the plate holder that are in the same set that is operative simultaneously being substantially mutually opposed in direction.

11. The improvement in an etching machine as in claim 9 in which the nozzles of the at least one array of spray nozzles mounted underneath are shaped to emit a substantially square spray pattern.

12. The improvement in an etching machine as in claim 9 in which the nozzles of the at least one array of nozzles mounted at each lateral side of the curved plate are directed toward thereto at about the horizontal direction.

References Cited UNITED STATES PATENTS 3,266,502 9/1964 Copeland l56-345 JACOB H. STEINBERG, Primary Examiner U.S. Cl. X.R. 

